The present invention relates to cardiac pacemakers and in particular to implantable cardiac pacemakers that are capable of being selectively programmed and/or externally interrogated.
Implantable cardiac pacemakers have been in existence since the later 1950's, although external pacemakers were known even earlier. Since that time great strides have been made in improving upon the leads and the pulse generators that together comprise the pacemaker. In particular, the pulse generator circuitry has evolved from discrete components to semi-custom integrated circuits, which are now fabricated from complimentary metal oxide semi-conductor (CMOS) technology or as with the present invention from integrated injection logic (I.sup.2 L) technology.
With this evolution, so too have digital techniques been applied to the design of the pulse generator circuitry, as well as techniques for non-invasively programming various of the pacing parameters and modes into the pulse generator. For example, see U.S. Pat. No. 4,304,238 with respect to a programmable parameter pacer. Alternatively, an example of a multi-mode programmable cardiac pacemaker can be found upon reference to U.S. Pat. No. 4,233,985. The pacemaker disclosed therein permits the operator to externally program various of the pacing parameters (i.e. rate, pulse width, pulse amplitude, refractory and sensitivity.) That pacemaker, however, can only be selectively programmed into either the ventricular demand (VVI), R-wave synchronous (VVT) or asynchronous modes of operation.
While the other multi-mode pacemaker accommodates a great many patients that require pacing in one of the other of these modes, there are a great many other patients that require pacing in other modes or for whom the necessary mode of operation may change with time, and which modes or mode changes are not accommodated via devices of the above type. These other desirable pacing modes are atrial demand (AAI), P-wave synchronous (AAT), P-wave synchronous demand (VDD), double demand synchronous (DDD) and A-V sequential (DVI).
The present invention, therefore was developed to permit an operator (1) to selectively program all of the above modes of pacer operation as well as for each of the various associated programmable parameters, (2) to selectively interrogate many of the analog and digital values that are accessible to the pulse generator circuitry and (3) to select a nominal parameter mode, that is dependent upon a number of pre-programmed nominal parameters. Further, the present invention provides the operator to the ability rate smooth and/or gracefully degradate the pacemaker output during conditions of high natural atrial rates.
The present invention, in one pulse generator, thus accommodates all the generally accepted modes of pacemaker operation, while introducing a great many other advantages and improvements. These advantages and improvements over the prior art will, however, become more apparent to those of skill in the art, upon a reading of the following description and upon reference to the appended drawings.